Resin composition and article molded therefrom

Abstract

The present invention relates to: a resin composition comprising a polyacetal resin (A), a salt (B) consisting of a carboxylic acid and an alkaline-earth metal, and a rubber-containing graft polymer (C); and a molded article formed by molding the resin composition. The resin composition and the molded article of the present invention are characterized in that the thermal decomposition associated with weight loss in a molding process or the formaldehyde in the molded article is reduced.

The invention claimed is: 
     
       1. A resin composition comprising
 a polyacetal resin (A), 
 a salt (B) consisting of a carboxylic acid having 10 to 36 carbon atoms and an alkaline-earth metal, wherein in the salt (B):
 pKa of the carboxylic acid is 4 to 5, 
 an amount of alkaline metals in the salt (B) is 50 ppm or less based on an amount of the salt (B), 
 a mass ratio of the alkaline-earth metal to the salt (B) in the resin composition is equal to or more than (a molecular weight of the alkaline-earth metal)/(a molecular weight of the salt (B)), and 
 a content of free carboxylic acid in the salt (B) is 0.2% or less based on the amount of the salt (B), and 
 
 a rubber-containing graft polymer (C) comprising sodium and/or potassium, wherein 
 when 2 parts by mass of the salt (B) consisting of a carboxylic acid and an alkaline-earth metal is dissolved in 18 parts by mass of deionized water comprising a nonionic dispersant, the obtained solution has pH 10 to 12, and 
 a content of sodium and potassium in the resin composition is 10 ppm or less. 
 
     
     
       2. The resin composition according to  claim 1 , wherein the alkaline-earth metal is calcium. 
     
     
       3. The resin composition according to  claim 1 , wherein the rubber-containing graft polymer (C) comprises one or more selected from the group consisting of a butadiene rubber and a styrene-butadiene copolymer rubber. 
     
     
       4. The resin composition according to  claim 1 , wherein
 a tensile yield value of the ISO-527 type 1A test piece formed by injection molding the resin composition at a molding temperature of 205° C., under conditions of a tension speed of 50 mm/min, is 28 MPa or more, and 
 an impact value of the resin composition at 25° C. according to Charpy impact test (notch tip radius: 0.25 mm±0.05 mm) is 12 kJ/m 2  or more. 
 
     
     
       5. The resin composition according to  claim 1 , wherein
 a content of the salt (B) is 0.1 to 2% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C), and 
 a content of the rubber-containing graft polymer (C) is 5 to 40% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C). 
 
     
     
       6. The resin composition according to  claim 1 , wherein a FOG value according to a VDA 278 test is 100 μg/g or less. 
     
     
       7. The resin composition according to  claim 1 , further comprising one or more hindered phenol-based antioxidants (D) selected from the group consisting of ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. 
     
     
       8. The resin composition according to  claim 7 , wherein a content of the hindered phenol-based antioxidant(s) (D) is 0.08 to 0.7 parts by mass based on a total of 100 parts by mass of the polyacetal resin (A), the salt (B) consisting of a carboxylic acid and an alkaline-earth metal, and the rubber-containing graft polymer (C). 
     
     
       9. A molded article formed by molding the resin composition according to  claim 1 . 
     
     
       10. A method for producing the resin composition according to  claim 1 , comprising mixing
 a polyacetal resin (A), 
 a salt (B) consisting of a carboxylic acid having 10 to 36 carbon atoms and an alkaline-earth metal wherein:
 pKa of the carboxylic acid is 4 to 5, 
 an amount of alkaline metals in the salt (B) is 50 ppm or less based on an amount of the salt (B), 
 a concentration (% by mass) of the alkaline-earth metal in the salt (B) is equal to or more than a (molecular weight of the alkaline-earth metals)/a molecular weight of the salt (B)), 
 a content of free carboxylic acid in the salt (B) is 0.2% or less based on the amount of the salt (B), and 
 
 a powder (Y) comprising a rubber-containing graft polymer (C) comprising sodium and/or potassium, in which the content of sodium and potassium of the powder (Y) is 50 ppm or less based on an amount of the powder (Y), wherein 
 when 2 parts by mass of the salt (B) consisting of a carboxylic acid and an alkaline-earth metal is dissolved in 18 parts by mass of deionized water comprising a nonionic dispersant, the obtained solution has pH 10 to 12. 
 
     
     
       11. The resin composition according to  claim 1 , wherein a content of the salt (B) is 0.4 to 2% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C). 
     
     
       12. The resin composition according to  claim 1 , wherein a content of a content of the salt (B) is 0.5 to 2% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C). 
     
     
       13. The resin composition according to  claim 1 , wherein a content of the rubber-containing graft polymer (C) is 9.5 to 40% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C). 
     
     
       14. The resin composition according to  claim 1 , wherein a content of the rubber-containing graft polymer (C) is 24 to 40% by mass in a total of 100% by mass of the polyacetal resin (A), the salt (B), and the rubber-containing graft polymer (C). 
     
     
       15. The method of  claim 10 , wherein the powder (Y) is recovered as powders by coagulating the rubber-containing graft polymer using a coagulant and is washed with deionized water in an amount of 10 or more times larger than the solid content of a latex of the rubber-containing graft copolymer (C) in order to remove sodium and potassium. 
     
     
       16. The method according to  claim 10 , wherein the method comprises, prior to the mixing, dispersing the powder (Y) in deionized water thereby producing a dispersion having pH of 6 to 12. 
     
     
       17. The method according to  claim 10 , wherein the method comprises, prior to the mixing, dispersing the powder (Y) in deionized water thereby producing a dispersion having pH of 7 to 8. 
     
     
       18. The method according to  claim 10 , wherein the method comprises, prior to the mixing, dispersing the powder (Y) in deionized water thereby producing a dispersion having pH of 6 to 7.2.